Well, it brings the usual web security issues to the desktop, dragging with it much of the browsers' attack surface. Also, there's been a bunch of CVE – there's one [0] in particular that springs to mind.

    Accessibility is only achieved by the creator's intention.

That's a problem. Native widgets come with accessibility built in (to the extent accessibility is supported on the platform in question).

[0]: https://www.trustwave.com/en-us/resources/blogs/spiderlabs-b...